In the last ten years, there has been a rapid growth of industry and residences into rural and isolated areas. Thus, more people are having to spend more time in what used to be rural and isolated areas. Since there are more people in these areas now, there is now a need for additional telephone support in these areas. For example, there is a need for pay phones throughout these areas to allow people to make telephone calls. Pay phones are phones in which a user pays for the call using money or credit cards and they are usually placed in public areas. The cellular pay phones are fixedly installed but are connected via radio signals to a cellular system, thus the term cellular pay phone. Debit phones are regular cellular phones with a prepaid number of call credits. Debit phones are typically used in markets where fraud or the occurrence of people not paying their bills is prevalent. Typically, pay phones are connected to land line systems by telephone cables. However, it can be very expensive to run new land line cables to isolated or rural areas which did not previously have land line telephone service. In addition, the cellular provider may want to provide pay phones in areas in which the cellular provider does not have a land line system. Furthermore, the cellular provider may want to provide cellular pay phones on public transportation vehicles such as trains or buses.
FIG. 1 illustrates a cellular communication system which can provide support for cellular pay phones and debit phones. FIG. 1 illustrates 10 cells, C1-10, of a cellular radio system. For each cell, there is a corresponding base station B1-B10. Remote stations which can either be cellular pay phones, debit phones, or regular cellular phones are shown as M1-M10. Some of the remote stations may be moved within a cell and from one cell to another. A mobile switching center MSC is connected to all of the base stations by cables or other fixed means, like radio signals. The MSC is also connected by cables or links to a fixed public telephone network or a similar fixed communication network. The MSC communicates with the remote stations by sending signals or commands to the base stations wherein the base stations transmit and receive the appropriate signals to and from the remote stations.
For pay phone/debit phone service, the pay phone/debit phone needs to know what rate to charge during the call. This charge rate information can be provided in several ways. For example, in some systems, the pay phones/debit phones can have a chart of different charge rates which are selected by analysis of the called numbers. The problem with this arrangement is that every time the system operators change the rates, the chart stored in each pay phone/debit phone needs to be upgraded.
In other systems, the charge rate information can be sent to the pay phones/debit phones so that the user will know how much money to deposit into the machine or how much money is going to be charged to a credit or debit card for the call or how many monetary units will be removed from the prepaid amount in the debit phone. There is also a need for authenticating the users of a pay phone. If a user is not authenticated or a simple authentication algorithm is used, the pay phones may be cloned or calls hi-jacked enabling people to make calls without being charged. Some analog AMPS (Advanced Mobile Phone Service system) operators have introduced pay phones into their cellular networks using Charge Rate Order messages (CRO) to send the charge rate information to the pay phone/debit phone. However, Authentication and Privacy functions, e.g. Authentication, disabling DTMF, and enabling/disabling encryption, are no longer available. The Charge Rate Order is a standard function in the TACS system which happens to also work in AMPS systems but only as a non-standardized proprietary function. In some systems, the Charge Rate Order is based upon giving the mobile phones a special subscriber category (MCH) which differentiates them from ordinary cellular subscriptions. When a call is made and the mobile switching center detects that the called party has answered the call, the MSC checks the MCH category of the originating phone. If the category indicates that the mobile phone is indeed a pay phone/debit phone, the CRO function within the MSC sends a message to the pay phone/debit phone through the appropriate base station indicating that the called party has answered the call and which charge rate is to be used during the call.
However, there are several problems with using charge rate order functions. First of all, the Charge Rate Order is a standard TACS function only and is not standardized in AMPS systems. Furthermore, when Authentication and Privacy was introduced into AMPS systems, spare Order Codes were used for Authentication which happens to coincide with the Order Codes that the TACS Charge Rate Order uses. Thus, the Charge Rate Order message can no longer be used to send the charge rates in AMPS systems without disabling Authentication and Privacy.
As noted above, the TACS system provides a Charge Rate Order function. In addition, the TACS system provides an Authentication function. However, the Authentication function uses a simpler security algorithm and does not provide the same level of protection against cloning. Furthermore, the TACS system does not provide message encryption (enabling/disabling).
As noted above, the AMPS systems do not support Charge Rate Orders. It is not practicable to introduce a specific dedicated message for this function in the AMPS system for several reasons. First of all, it would require upgraded software not only in the mobile service centers and remote stations, but also in radio base stations. That is all old base stations where a pay phone is to be connected would have to be upgraded. Furthermore, a debit phone roaming into an area served by old, non-upgraded base stations, would not work. Furthermore, it takes time to standardize and implement new messages. Thus, there is a need for a solution where only the MSC software and the pay/debit phones need to be upgraded in order to provide appropriate cellular coverage without disabling the authentication capability.